Take a Journey of Discovery with RXTE - Classroom Activity

Black Holes

A black hole is a region of space from which neither radiation (light)
nor matter can escape. We can most easily detect them when they are in a
binary star system. This means the black hole has a "normal" star in orbit
around it. The black hole has a gravitational field that is so strong that
matter is pulled off the companion star into a disk that rotates around
the black hole.

This rotating disk of matter is called an accretion disk.
As the matter from the accretion disk comes close to the event horizon,
or outer limit, of the black hole, it heats up to millions of degrees in
temperature, releasing X-rays.

A black hole is an endpoint of stellar evolution. When a massive
star dies, it will explode violently. This explosion is called a supernova.
If the star had enough mass left before it died, it will be collapsed by
its own gravity and become a black hole. A black hole resulting from
a supernova explosion will have a mass greater than 3 times the mass of the
Sun. If the object created by the explosion has between 1.4 and 3 solar
masses, it will actually be a neutron star. But if the object has more
than 3 solar masses, not even the tightly packed neutrons that make up
the neutron star can withstand the star's gravitational pull, and a black
hole will be created.